Power transistors (e.g., metal oxide semiconductor field effect transistors (MOSFETs), insulated gate bipolar transistors (IGBTs), superjunction MOSFETs, vertical metal oxide semiconductor (VMOS) transistors, vertical double-diffused metal oxide semiconductor (VDMOS) transistors, bipolar junction transistors, etc.) are often characterized by a number of device characteristics. For example, a relatively high breakdown voltage (BV), a relatively low on-resistance (RON), a relatively large safe operating area (SOA), and/or the like are generally desirable.
In power transistors, there is typically a trade-off between high BV and low RON characteristics. For example, BV and RON characteristics both typically increase as dopant concentration in a transistor's drift regions decrease or the thickness of the drift regions increase. In certain transistors, such as over-current protection transistors, over-voltage protection transistors, power supply switching transistors, normally on transistors, depletion mode transistors, performance transistors, etc., BV and RON characteristics may be particularly important. For example, it may be beneficial for such transistors to have BV characteristics sufficient to block excess voltage during an over-voltage condition and to have low RON such that little power is dissipated by the transistor.
Further, relatively low cost and relatively high yield are also generally desirable attributes for fabrication of a transistor. In many cases, costs increase and yields decrease as transistor fabrication becomes more complex. Some of the many factors leading to fabrication complexity include the number of processes employed (e.g., deposition, diffusion, etching, masking, etc.), tolerances for employed processes, and/or the like.